Abstract
The cold air supply system, in which temperature difference between the supply and the return air is higher than usual system, has been applied to the office buildings. It is because that the cold air supply system can save energy for air transport and space for air ducts and the ice storage system by using nighttime electricity can be used for the heat source. The cold air supply system has been mainly studied by experiments and field measurements. Few Computational Fluid Dynamics (hereafter CFD) simulations was applied to that system because it was difficult to reproduced the complex airflow around the air diffuser in the CFD simulation. However the Prescribed Velocity Method (hereafter P.V. method) can simulate the airflow around the air diffuser with coarse grids system. In the previous paper, it was reported that CFD simulation using P.V. method showed good agreement with experimental results for Ceiling Air Diffuser. In this paper, measurements were carried out under non-isothermal conditions in the test room. The applicability of the isothermal airflow data to a non-isothermal CFD simulation was examined using local Archimedes number. M.I. Grimilyn et al. proposed that the buoyancy effect is not significant if the local Archimedes number at the box surface is lower than 0.1. The local Archimedes number was very small at virtual box surfaces and the isothermal airflow data can be applied to the non-isothermal simulation as the boundary condition. CFD simulations using the unstructured grid system were conducted to obtain airflow data around the high diffusion type ceiling air diffuser as boundary conditions of coarse grid CFD. In addition, the coarse grid CFD with P.V. method using the airflow data around the diffuser was compared to the result of the unstructured CFD simulations under isothermal conditions. The result of the coarse grid CFD with P.V. method showed good agreement with the one simulated using unstructured grid system. Furthermore, measurements were compared to the non-isothermal coarse grid CFD using P.V. method with the isothermal airflow data around the diffuser. The air and temperature distributions of CFD and experiment were similar except for the certain parts of the test room.
